1. Field of the Invention
The present invention relates generally to satellite receiver systems, and in particular, to signal distribution of multiple satellite signals.
2. Background of the Related Art
In modern and competitive TV delivery systems it is necessary to provide customers with the ability to simultaneously and independently tune to and receive any of the available TV channels from a multiplicity of satellites transmitting transponder channels. In a typical satellite system, a frequency band may have two different signal polarizations, thus delivering the multiplicity of transponder channels through the multiplicity of satellite paths simultaneously on the same frequency band. A multiplicity of different TV appliances, such as TV sets, set-tops, personal video recorders (PVRs), digital video recorders (DVRs) and other devices need to receive different TV programs simultaneously in different rooms in one household (the “whole-home video” or “watch and record” capability), or in a multiplicity of households in the case of multiple-dwelling units. It is a challenge to provide the capability of reception of any channel from any path on multiple tuners in different receive appliances simultaneously and independently. This problem of enabling each tuner to independently tune to any channel from either polarization of any satellite has been resolved in the prior art by the means of frequency “band translation switch” (BTS) technology as well as “channel-stacking switch” (CSS) technology utilizing secondary frequency conversion, as described below.
FIG. 1 shows a typical block diagram of a satellite band translation system of the prior art for use with two satellites, providing two outputs, each feeding a dual channel tuner (or two individual tuners). Each antenna receives two signals of different polarizations, typically having channel frequencies offset by half-channel width or having the same channel frequencies. In direct broadcast satellite (DBS) applications, the polarization is typically circular, having right-hand (R1 and R2) and left-hand (L1 and L2) polarized signals as labeled in FIG. 1. Signals can also be linearly polarized with horizontal and vertical polarizations.
The received signals are processed in a well known low noise block-converter (LNB) 8 consisting of low noise amplifiers 7, which typically comprise 2 or 3 amplifiers in a cascade, filters 9, which typically comprise bandpass filters providing image rejection and reducing out of band power, and frequency converter block 10. The converter block 10, performing frequency downconversion, contains local oscillators LO1 14 and LO2 12 typically of the dielectric-resonator oscillator (DRO) type, mixers, and post-mixer amplifiers. The two mixers driven by LO1 downconvert the signals to one frequency band (lower, L) while the mixers driven by LO2 downconvert to a different frequency band (higher, H). The L and H frequency bands are mutually exclusive, do not overlap, and have a frequency guard-band in between. The L and H band signals are then summed together in a separate combiner 16 in each arm, forming a composite signal having both frequency bands, “L+H”, which is often referred to as a “band-stacked signal”, which is then coupled to a 2×4 matrix switch/converter block 20.
The matrix switch 30 routes each of the two input signals to selected one or more of the 4 outputs, either by first frequency converting the signals in the mixers 28 driven by LO3 32 or directly via the bypass switches around the mixers. The controls for the switch and mixer bypass are not shown in the figure. The frequency of the LO3 is chosen such that the L-band converts into the H band, and vice versa, which is referred to as the “band-translation”. This is accomplished when the LO3 frequency is equal to the difference of the LO2 and LO1 frequencies. The band-translation is a second mixing and frequency conversion operation performed on the received satellite signal, after the first frequency conversion operation performed in the LNB.
The outputs of the matrix switch/converter block 20 are coupled through diplexers consisting of a high-pass filter 22, low-pass filter 24 and a combiner 26, with two similar paths providing two dual tuner outputs 18 and 34. The filters 22 and 24 remove the undesired portion of the spectrum, i.e. the unwanted bands in each output. Each of the two outputs 18 and 34 feeds a dual tuner set top box (STB) via a separate coaxial cable, for a total capability of 4 tuners in STBs. By controlling the matrix switch routing and the mixer conversion/bypass modes, a frequency translation is accomplished and each of the 4 tuners can independently tune to any of the channels from either polarization of either satellite.
FIG. 2 is a prior art block diagram of a satellite band translation system receiving two satellites like FIG. 1, but with additional capability of receiving and processing an external input signal 36. In FIG. 2 an exemplary case of a common Ku band radio frequency (RF) downlink frequency band as well as a standard intermediate frequency (IF) band is shown. In the example, the downlink Ku frequency band 12.2 GHz to 12.7 GHz is downconverted to a standard satellite IF frequency range 950-2150 MHz by mixing with two local oscillators LO1 and LO2. The LO1 frequency is 11.25 GHz, downconverting the right-hand polarized signal R1 to a low band 950 MHz to 1450 MHz (L) and LO2 is 14.35 GHz, downconverting the left-hand polarized signal L1 to a high band 1650 MHz to 2150 MHz (H). Combining the two, a band-stacked composite signal (“L+H”) is formed, spanning from 950 MHz to 2150 MHz, with a guard band 200 MHz wide in the middle. The same is repeated for the other two signals, R2 and L2. The external input signal 36 comes already converted and band-stacked in the standard IF range 950-2150 MHz, typically from another antenna/LNB. A 3×4 matrix switch 38 is used in order to multiplex the additional external signal with the other two internal signals.
FIG. 3 is a block diagram of a satellite band translation system of the prior art for receiving input from two satellites and supporting one external input like FIG. 2, but providing one more output, for a total of three outputs capable of independently feeding three dual tuners. To accommodate increased number of output ports, a larger matrix switch of a 4×6 size is used.
These and other prior art systems, while accomplishing the goal of independent tuning of multiplicity of tuners, achieve that by employing a secondary frequency conversion, effectively adding one more conversion to the conversion already occurring in the LNB, thus not only increasing the complexity, but potentially degrading the signal quality as well. Furthermore, if the switch-over in the matrix switch creates a transient and results in a change of level and phase of the received signal, interruption and temporary loss of service can occur at the affected port.
U.S. Pat. No. 6,408,164 issued to Lazaris-Brunner et al entitled “Analog Processor for Digital Satellites”, incorporated herein by reference, describes an analog processor for use with digital satellites. The patent discloses a system that consists of a receiver block that performs a frequency down-conversion, an N×M Switch Matrix, followed by another frequency down-conversion.
U.S. Pat. No. 7,130,576 issued to Gurantz et al entitled “Signal Selector and Combiner for Broadband Content Distribution”, incorporated herein by reference, describes a processor for use with digital satellites. The patent discloses a system that consists of low noise block converters (LNBs) that perform a frequency down-conversion, an N×M Switch Matrix, followed by another frequency down-conversion.
The prior art leaves room for improvements, such as reducing the complexity, power and cost, preserving the phase noise performance as well as addressing the switch-over transient effects thus eliminating the risk of service interruption.